qt TxDialog: visibility of widgets should be set after parenting

widget.show() and widget.setVisible(True) results in a blink of an ephemeral window containing the widget;
that is, unless the widget has a parent explicitly set or it can be determined via which layout the widget is placed in.

electrum/gui/qt/transaction_dialog.py

@@ -558,8 +558,6 @@ class BaseTxDialog(QDialog, MessageBoxMixin):
         self.rbf_cb = QCheckBox(_('Replace by fee'))
         self.rbf_cb.setChecked(bool(self.config.get('use_rbf', True)))
         vbox_right.addWidget(self.rbf_cb)
-        self.rbf_label.setVisible(self.finalized)
-        self.rbf_cb.setVisible(not self.finalized)
 
         self.locktime_label = TxDetailLabel()
         vbox_right.addWidget(self.locktime_label)
@@ -572,6 +570,10 @@ class BaseTxDialog(QDialog, MessageBoxMixin):
 
         vbox.addLayout(hbox_stats)
 
+        # set visibility after parenting can be determined by Qt
+        self.rbf_label.setVisible(self.finalized)
+        self.rbf_cb.setVisible(not self.finalized)
+
     def set_title(self):
         self.setWindowTitle(_("Create transaction") if not self.finalized else _("Transaction"))